Manufactured printed circuit boards (PCBs) often contain design or manufacturing errors. These printed circuit boards may be scrapped or they may be reworked to correct these errors.
One of the most known methods for reworking printed circuit boards is to solder yellow wire jumper cables, also referred to as discrete wires, between surface points on the printed circuit board to interconnect those points. In addition, improper internal and surface connections in the printed circuit board may be broken by drilling holes through the board severing those connections. This is a process normally done by hand and is time consuming, expensive and error prone. For example, a person reworking the circuit board may solder the yellow wire to an incorrect location on the printed circuit board or may damage the printed circuit during the soldering process. However, this method of reworking continues to be one of the most prevalent methods used today.
A method taught in IBM Technical Disclosure Bulletin entitled "Engineering Change Method and Hardware" (Vol. 29, No. 7, p. 2953, Dec. 1986) utilizes gluing a smaller auxiliary printed circuit board onto the original printed circuit board and connecting the auxiliary printed circuit board to the original printed circuit board with yellow wire jumper cables. This allows the user the capability of providing additional wiring and/or devices on the auxiliary printed circuit board. However, this process utilizes a large area of surface real estate on the original printed circuit board and the soldering process is error prone as described above.
Another technique is described in U.S. Pat. No. 4,742,431 and IBM Research Disclosure entitled "Surface Mounted Technology Card Rework with Flexible Applique" (No. 335, Mar. 1992) wherein a flexible auxiliary wiring board is attached to the printed circuit board similar to the auxiliary printed circuit board described above. This technique allows the user to provide additional wiring and/or devices on the auxiliary wiring board. However, the thinner material used in the auxiliary wiring board allows for soldering the wiring from the auxiliary board directly to the underlying printed circuit board or to devices located on the underlying printed circuit board.
A recent technique for adding selected circuit lines to the surface of a printed circuit board involves screen printing a thin conducting polymer line across the surface of a printed circuit board contacting preexisting circuit points at either end of the polymer line. This technique also provides the capability of adding additional bonding pads.
In EPO 126171 and IBM Technical Disclosure Bulletin entitled "Printed-Circuit Card Rework Process" (Vol. 15, No. 1, pp. 246-247, June 1972), in a technique called subtractive etch, the outside circuit layer of the printed circuit board may be completely reworked. The outside circuit layer is completely milled or etched off. An auxiliary circuit layer is then laminated or deposited onto the etched printed circuit board. One of the primary disadvantages of this technique is that the subtractive etch process is difficult to control and may excessively mill or etch back into other underlying circuitry.